Such a sensor system is already part of the prior art and contains a sensor body, a sensor element, arranged at the sensor body for contactlessly measuring the distance between itself and an object, a control unit, for supplying a measuring voltage to the sensor element and for evaluating the measuring voltage for the purpose of determining the distance, and a cable, between the sensor body and the control unit, which is used for transmitting the measuring voltage.
The sensor system is capable of measuring the distance between the sensor element and the object, for example, by capacitive or inductive means, if it is a metallic object, or by optical or acoustical means depending on the system configuration.
If the sensor body of the sensor system is permanently joined to a tool, it is possible to position the tool relative to the object or workpiece in order to be able to machine the workpiece in a suitable manner. Positioning occurs via a control device which receives the measured distance as an actual value and controls the position of the sensor body or the tool by comparing the actual value with a predetermined set tip.
The tool can be, for example, a laser cutting unit for generating a laser beam by means of which the workpiece can be cut or otherwise treated.
At the beginning of the development of sensor systems of this type, not only the sensor element but also a large proportion of the sensor electronics were located inside the sensor body. If, therefore, the sensor body was separated from the control unit by detaching the cable, the control unit was able to detect this unambiguously. In such a case, it generated a warning signal, by means of which the control device for positioning the sensor body was deactivated or stopped.
Integrating the sensor electronics in the sensor body, however, entailed a number of disadvantages. Thus, there was only little space inside the sensor body for installing the electronic components. Installing and calibrating these electronic components was therefore very time-consuming and thus represented a considerable cost factor. Due to the space required for installing the electronic components, the design of the nozzle body was much more elaborate, which also entailed additional costs. Furthermore, integrating the electronic components in the sensor body constituted an obstacle to making the sensor body as slender as possible, which is required, in particular, when the workpiece or object is to be machined three-dimensionally under restricted spatial conditions. There is also the risk of a temperature drift of the actual value or measurement value supplied by the sensor body due to the sensor electronics heating up too much inside the sensor body which is subject to very great heating when it operates in conjunction with a laser cutting tool and is positioned in the immediate vicinity of the cutting track.
Due to the above disadvantages, the decision was made to arrange the complete sensor electronics at a very great distance from the sensor body. More accurately, the sensor electronics were connected to the sensor body by means of a cable several meters in length, which could also be shielded. The shielding could also be carried out actively, which means that the measurement signal present at the sensor element is applied to the shielding via a capacitor and an amplifier having a gain of V which is equal to 1.
If the sensor electronics are now separated from the sensor body by detaching the cable, however, this leads to a misinterpretation of the actual value by the control unit. In such a case, the control unit detects a very large actual value or distance which is much greater than the normal operating distance, so that it attempts to reduce this distance again. This involves the considerable risk that the sensor element and the sensor body run against the object or workpiece, which could lead to damage.
If, for example, this is a capacitively operating sensor system, the separation of the cable from the sensor body leads to the control unit detecting only a severely reduced measuring capacitance, since the signal line of the cable is now free. However, this effect also rises when the distance between the sensor body of the sensor element and the object or workpiece is much greater than the normal working distance. For this reason, it is not possible to generate an unambiguous warning signal from the measurement signal.